A FeRAM (or FRAM) using a ferroelectric material having spontaneous polarization is a memory that stores “1” and “0” bits using remanent polarization and has attracted attention as a next-generation memory device since it has a lot of advantages such as low power consumption, rapid processing speed, and a simple configuration. The FeRAM stores information in two different types: a capacitor type (1 Transistor-1 capacitor type) in which a dielectric material of a capacitor of a DRAM is simply substituted by a ferroelectric material; and a transistor type (1 Transistor type) in which a gate dielectric film is substituted by a ferroelectric material. A capacitor-type device is a nonvolatile device but destroys data while reading the data, and, thus, the capacitor-type device needs to store the data again after reading the data. However, a transistor-type memory device can maintain data after reading the data and a single transistor serves as a memory device. Therefore, the transistor-type device has an advantage over the capacitor-type device in view of integration. Meanwhile, it is difficult to form a stable interface between a ferroelectric material and a semiconductor material, and, thus, a further study on a structure employing a dielectric film (MFIS structure) or a metal film and a dielectric film (MFMIS) serving as a buffer layer between the ferroelectric material and the semiconductor material is needed. As a material used for the buffer layer, a conductive material and an insulating material can be selectively used as necessary, and Pt, RuOx or IrOx may be used as the conductive material and an oxide such as TiO2, SrTiOx, ZrO2, LiNbO3 or Al2O3 may be used as the insulating material.
Flexible electronics have attracted considerable attention over the last decade owing to their range of applications, such as smart cards, biomedical sensors, and foldable antennas. To realize these applications, the development of flexible nonvolatile memory devices for data storage or radio-frequency transponders is required. Most flexible nonvolatile memory reported to date demonstrated organic materials, including small molecules and polymer organics because of their good mechanical bendability. However, a low degree of crystallinity associated with classes of materials results in relatively low performance of the as-fabricated devices. On the other hand, recent effort to address this issue explores a direct formation of high-quality inorganic materials onto plastic substrates through a sol-gel process to construct flexible memory with high performance. However, types of materials suitable for this process are limited.